Pesticide tolerant and phosphorus solubilizing Pseudomonas sp. strain SGRAJ09 isolated from pesticides treated Achillea clavennae rhizosphere soil

Biodegradation of monocrotophos by Brucella intermedia Msd2 isolated from cotton plant

Widespread and inadequate use of Monocrotophos has led to several environmental issues. Biodegradation is an ecofriendly method used for detoxification of toxic monocrotophos. In the present study, Msd2 bacterial strain was isolated from the cotton plant growing in contaminated sites of Sahiwal, Pakistan. Msd2 is capable of utilizing the monocrotophos (MCP) organophosphate pesticide as its sole carbon source for growth. Msd2 was identified as Brucella intermedia on the basis of morphology, biochemical characterization and 16S rRNA sequencing. B. intermedia showed tolerance of MCP up to 100 ppm. The presence of opd candidate gene for pesticide degradation, gives credence to B. intermedia as an effective bacterium to degrade MCP. Screening of the B. intermedia strain Msd2 for plant growth promoting activities revealed its ability to produce ammonia, exopolysaccharides, catalase, amylase and ACC-deaminase, and phosphorus, zinc and potassium solubilization. The optimization of the growth parameters (temperatures, shaking rpm, and pH level) of the MCP-degrading isolate was carried out in minimal salt broth supplemented with MCP. The optimal pH, temperature, and rpm for Msd2 growth were observed as pH 6, 35 °C, and 120 rpm, respectively. Based on optimization results, batch degradation experiment was performed. Biodegradation of MCP by B. intermedia was monitored using HPLC and recorded 78% degradation of MCP at 100 ppm concentration within 7 days of incubation. Degradation of MCP by Msd2 followed the first order reaction kinetics. Plant growth promoting and multi-stress tolerance ability of Msd2 was confirmed by molecular analysis. It is concluded that Brucella intermedia strain Msd2 could be beneficial as potential biological agent for an effective bioremediation for polluted environments.

Unraveling the potential of pesticide-tolerant Pseudomonas sp. augmenting biological and physiological attributes of Vigna radiata (L.) under pesticide stress

In the agricultural domain, chemical pesticides are repetitively and harshly used to kill harmful pests, but they often pose a serious threat to microbial diversity, soil fertility and agricultural output. To deal with these problems, pesticide-tolerant plant growth promoting (PGP) rhizobacterial strains are often used to combat pesticidal toxicity. Here, Pseudomonas sp. PGR-11 (accession no. OM348534), recovered from a Vigna radiata (L.) rhizosphere, produced various growth regulating (GR) substances, including indole-3-acetic acid (IAA; 82.5 ± 9.2 μg mL^-1), enzyme 1-aminocyclopropane 1-carboxylate (ACC) deaminase (μM α-ketobutyrate mg^-1 protein h^-1), siderophores and ammonia. Strain PGR-11 grew well when cultured in growth medium with added metalaxyl (MTXL; 1200 μg mL^-1), carbendazim (CBZM; 800 μg mL^-1) and tebuconazole (TBZL; 1600 μg mL^-1). Pseudomonas sp. synthesized PGP substances even in the presence of increasing doses of pesticides. The phytotoxicity of the tested pesticides was assessed both in vitro and under pot-house conditions using a Vigna radiata (L.) crop. Increasing concentrations of chemical pesticides negatively impacted the growth, physiological and biochemical features. However, pesticide-tolerant Pseudomonas sp. relieved the toxicity and improved the biological attributes of the plant. Bio-inoculated plants showed significant enhancement in germination attributes, dry biomass, symbiotic features and yield features when compared to un-inoculated ones. Furthermore, with 100 μg metalaxyl kg^-1 soil, strain PGR-11 increased the chl-a, chl-b, total chlorophyll, carotenoids, SPAD index, photosystem efficiency (Fv/Fm), PSII quantum yield (FPSII), photochemical quenching (qP) and non-photochemical quenching (NpQ) content by 12, 19, 16, 27, 34, 41, 26, 29 and 33%, respectively, over un-inoculated but pesticide-treated plants. Additionally, inoculation of Pseudomonas sp. with 100 μg tebuconazole kg^-1 soil caused a significant (p ≤ 0.05) enhancement in transpiration rate (E), stomatal conductance (g _s), photosynthetic rate (P _N), vapor pressure deficit (kPa) and internal CO₂ concentration (C _i) of 19, 26, 23, 28 and 34%, respectively. Conclusively, the power to tolerate abnormally high pesticide concentration, the capacity to produce/secrete PGP substances even in a pesticide-stressed medium and the potential for improving/increasing the growth and physiology of plants by pesticide detoxification makes Pseudomonas sp. PGR-11 a fascinating choice for augmenting the productivity of V. radiata (L.) even in pesticide-stressed soils. The current findings will be helpful for exploring pesticide-tolerant ACC-deaminase-positive microbial strains as gifted entities for the environmental bioremediation of pesticides.

A comprehensive synthesis unveils the mysteries of phosphate-solubilizing microbes

Phosphate-solubilizing microbes (PSMs) drive the biogeochemical cycling of phosphorus (P) and hold promise for sustainable agriculture. However, their global distribution, overall diversity and application potential remain unknown. Here, we present the first synthesis of their biogeography, diversity and utility, employing data from 399 papers published between 1981 and 2017, the results of a nationwide field survey in China consisting of 367 soil samples, and a genetic analysis of 12986 genome-sequenced prokaryotic strains. We show that at continental to global scales, the population density of PSMs in environmental samples is correlated with total P rather than pH. Remarkably, positive relationships exist between the population density of soil PSMs and available P, nitrate-nitrogen and dissolved organic carbon in soil, reflecting functional couplings between PSMs and microbes driving biogeochemical cycles of nitrogen and carbon. More than 2704 strains affiliated with at least nine archaeal, 88 fungal and 336 bacterial species were reported as PSMs. Only 2.59% of these strains have been tested for their efficiencies in improving crop growth or yield under field conditions, providing evidence that PSMs are more likely to exert positive effects on wheat growing in alkaline P-deficient soils. Our systematic genetic analysis reveals five promising PSM genera deserving much more attention.

Influence of plant beneficial Stenotrophomonas rhizophila strain CASB3 on the degradation of diuron-contaminated saline soil and improvement of Lactuca sativa growth

Diuron is one of the major hazardous pollutants which posses severe risk to the environment and human healthiness. On the other hand, salinity is the most severe environmental stressor that limits crop productivity. Therefore, it is required to address this co-existing abiotic stresses in agricultural soil. Plant growth-promoting rhizobacteria have gained an engaging role in the degradation of pesticides in agricultural soil. However, their role against the restoration of diuron-contaminated saline soil is still not known. Thus, in this study, diuron-degrading, salinity-tolerant Stenotrophomonas rhizophila strain CASB3 was isolated and characterized. Strain CASB3 showed important PGP traits under normal and diuron or salt stresses. Complete degradation of 10-50 mg L-1 diuron in the aqueous medium under normal and salinity stress conditions was achieved within 48-120 h and 48-192 h, respectively. A unique pathway for diuron biodegradation was proposed based on GC-MS analysis. In a greenhouse study, CASB3 inoculated into diuron-contaminated saline soil efficiently degraded diuron (50 mg kg-1) by 94% in 42 days and simultaneously resulted in an enhancement of root-shoot length (47.22-63.41%), fresh-dry biomass (136.36-156.66%), and photosynthetic pigments (36.93-92.28%) in Lactuca sativa plants. These results suggest the strain CASB3 could be used as a bioresource for the reclamation of diuron-contaminated saline soils.

Effect of endosulfan tolerant bacterial isolates (Delftia lacustris IITISM30 and Klebsiella aerogenes IITISM42) with Helianthus annuus on remediation of endosulfan from contaminated soil

Endosulfan contaminated soil has become an important risk to the environment and human health worldwide. In the present study, endosulfan tolerant bacterial strain Delftia lacustris IITISM30 and Klebsiella aerogenes IITISM42 were isolated from pesticide stressed agricultural soil and tested for plant growth promoting activities. A pot experiment was performed using Helianthus annuus, grown in soil supplemented with endosulfan and inoculated with pure and consortium of bacterial strain IITISM30 and IITISM42. Inoculation increased plant biomass production and endosulfan degradation, maximum degradation (90% at 5 mg kg^-1 of soil) was observed by inoculation with a consortium of bacterial strain IITISM30 and IITISM42. Moreover, there was significantly less endosulfan accumulation was observed in roots and shoots of bacterial inoculated plants as compared to uninoculated plants. Decrease in production of malonialdehyde (MDA) was noticed on inoculation of a bacterial strain. The study demonstrated that inoculation of a consortium of endosulfan tolerant plant growth promoting bacterial isolates could more effectively remediate endosulfan contaminated soils and decrease endosulfan residues in plants, than individual strains. Moreover, it revealed that combined use of H. annuus and endosulfan tolerant bacterial isolates IITISM30 and IITISM42 has great potential for remediating endosulfan contaminated soil.

Effects of organochlorine pesticides on plant growth-promoting traits of phosphate-solubilizing rhizobacterium, Paenibacillus sp. IITISM08

The study aimed to identify an effective phosphate-solubilizing and organochlorine pesticide-tolerant bacterial strain(s). A total of 50 phosphate-solubilizing bacterial (PSB) strains were isolated from pesticide-stressed soil. Ten isolates showing higher solubilization were selected for organochlorine pesticides (endosulfan, aldrin, and lindane) tolerance. The strain IITISM08 showed the maximum potential of phosphorous solubilization in Pikovaskya agar medium (solubilization index = 3.2) and in broth medium (348 ± 2 μg mL^-1) and tolerated up to 250 μg mL^-1 of organochlorine pesticides. During phosphorous solubilization, the presence of functional group and organic acid production were also observed using FT-IR and HPLC. The plant growth-promoting (PGP) traits of the strain IITISM08 was highly inhibited in presence of endosulfan among the three organochlroine pesticides. The strain IITISM08 degraded aldrin (79%), lindane (68%), and endosulfan (51%) at a concentration of 50 μg mL^-1. The strain IITISM08 was identified using 16S rDNA gene sequencing as Paenibacillus sp. (IITISM08). The study revealed that the strain IITISM08 can be used as PGP candidate even under organochlorine pesticide-stressed condition.

Endosulfan Degradation by Selected Strains of Plant Growth Promoting Rhizobacteria

Sixty endosulfan tolerant bacterial strains were isolated from pesticide stressed agricultural soils. Five most tolerant strains were tested for plant growth promoting (PGP) activities and endosulfan degradation under different optimizing conditions in broth and soil. The strains PRB101 and PRB77 were the most efficient in terms of endosulfan degradation and PGP activities and showed solubilization indexes of 3.3 and 3.1 mm, indole acetic acid production of 71 and 68 μg mL^-1, siderophore zones of 13 mm each at the recommended dosage, respectively. Hydrogen cyanide and ammonia production remained unaffected in the presence of endosulfan. PRB101 and PRB77 strains were able to degrade 74% and 70% of endosulfan in broth and 67% and 63% in soil, respectively. Based on 16S rDNA analysis, the strains PRB101 and PRB77 exhibited 99% homology with Bacillus sp. KF984414 and Bacillus sp. LN849696, respectively.

Biodegradation of 4-nitroaniline by plant-growth promoting Acinetobacter sp. AVLB2 and toxicological analysis of its biodegradation metabolites

4-nitroaniline (4-NA) is one of the major priority pollutants generated from industrial productions and pesticide transformation; however very limited biodegradation details have been reported. This work is the first to report 4-NA biodegradation kinetics and toxicity reduction using a newly isolated plant-growth promoting bacterium, Acinetobacter sp. AVLB2. The 4-NA-dependent growth kinetics parameters: μmax, Ks and Ki, were determined to be 0.039 h(-1), 6.623 mg L(-1) and 25.57 mg L(-1), respectively using Haldane inhibition model, while the maximum biodegradation rate (Vmax) of 4-NA was at 0.541 mg L(-1) h(-1) and 0.551 mg L(-1) h(-1), following Michaelis-Menten and Hanes-Woolf models, respectively. Biodegradation pathway of 4-NA by Acinetobacter sp. AVLB2 was proposed, and successfully led to the reduction of 4-NA toxicity according to the following toxicity assessments: microbial toxicity using Escherichia coli DH5α, phytotoxicity with Vigna radiata and Crotalaria juncea, and cytogenotoxicity with Allium cepa root-tip cells. In addition, Acinetobacter sp. AVLB2 possess important plant-growth promoting traits, both in the presence and absence of 4-NA. This study has provided a new insight into 4-NA biodegradation ability and concurrent plant-growth promoting activities of Acinetobacter sp. AVLB2, which may indicate its potential role for rhizoremediation, while sustaining crop production even under 4-NA stressed environment.